In general, in a fixing device for use in an electrophotographic image forming apparatus such as a copier and a laser printer (hereinafter, also simply referred to as “image forming apparatus”), a pair of heated rotating bodies such as a roller and a roller, a film and a roller, a belt and a roller, a belt and a belt are pressure contacted. Into the pressure contact part formed between the rotating bodies (hereinafter referred to as “fixing nip part”), a recording medium such as paper which holds an image formed of an unfixed toner (hereinafter referred to as “unfixed toner image”) is introduced, so that the unfixed toner is heated and melted. Consequently the image is fixed on the recording medium. The rotating body with which the unfixed toner image on the recording medium comes into contact is referred to as a fixing member. The fixing member is referred to as a fixing roller, a fixing film, or a fixing belt, according to the form.
Examples of the known fixing member include a laminate having an elastic layer which contains a silicone rubber or a fluorine rubber and a releasing layer which contains a fluorine resin such as tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) arranged on a substrate formed of a metal or a heat-resistant resin in this order (Patent Literature 1).
The elastic layer in the fixing member having such a structure has a function for allowing the fixing member to follow the irregularities on a paper surface.
Namely, in formation of an electrophotographic image on a sheet of paper having relatively large irregularities on the surface (so-called rough paper), unevenness in glossiness may occur in the electrophotographic image when the surface of the fixing member cannot sufficiently follow the irregularities. The reason is that the unfixed toner placed on a protrusion on the paper surface is well squashed by the fixing member, while the unfixed toner placed on a concave on the paper surface is fixed without being sufficiently squashed. As a result, the image formed on the concave on the paper surface has a lower glossiness in comparison with the image formed on the protrusion on the paper surface, so that an electrophotographic image having unevenness in glossiness is produced. The elastic layer of the fixing member has a function for imparting flexibility to the surface of the fixing member coming into contact with irregularities, such that the surface is deformed to follow the irregularities.